Corrosion occurs when metals are oxidized to their respective ions and/or insoluble salts. For example, corrosion of metallic iron can involve conversion to soluble iron in a +2 or +3 oxidation state or insoluble iron oxides and hydroxides. Also, corrosion has a dual nature in that a portion of the metal surface is removed, while the formation of insoluble salts contributes to the buildup of deposits. Losses of metal cause deterioration of the structural integrity of the system. Eventually leakage between the water system and process streams can occur.
Corrosion of iron in oxygenated waters is known to occur by the following coupled electrochemical processes:
1. Fe.sup.0 .fwdarw.Fe.sup.+2 +2e.sup.- (Anodic Reaction) PA1 2. O.sub.2 +2e.sup.- .fwdarw.2OH.sup.- (Cathodic Reaction) PA1 React directly with Fe.sup.+2 causing it to precipitate; PA1 Facilitate the oxidation of Fe.sup.+2 to Fe.sup.+3, compounds of which are typically less soluble; or, PA1 Promote the formation of insoluble Fe.sup.+3 compounds. PA1 (a) acrylic acid 40-90, more preferably 40-80, and most preferably 60-80 PA1 (b) methacrylic acid 5-30, more preferably 10-30, and most preferably 10-20 PA1 (c) t-butyl acrylamide 5-50, more preferably 10-30, and most preferably 10-20 PA1 CH.sub.3 PO.sub.3 H.sub.2 PA1 CH.sub.3 CH.sub.2 PO.sub.3 H.sub.2 PA1 C.sub.6 H.sub.5 CH.sub.2 PO.sub.3 H.sub.2 ##STR7## wherein R.sub.1 is an alkylene having from about one to about 12 carbon atoms or a substituted alkylene having from about 1 to about 12 carbon atoms, e.g., hydroxyl, amino etc. substituted alkylenes, and M is as earlier defined above. PA1 H.sub.2 O.sub.3 P--CH.sub.2 --PO.sub.3 H.sub.2 PA1 H.sub.2 O.sub.3 P--CH(CH.sub.3)PO.sub.3 H.sub.2 PA1 (CH.sub.3).sub.2 C(PO.sub.3 H.sub.2).sub.2 PA1 H.sub.2 O.sub.3 P--(CH.sub.2).sub.3 --PO.sub.3 H.sub.2 PA1 H.sub.2 O.sub.3 P--(CH.sub.2).sub.10 --PO.sub.3 H.sub.2 PA1 H.sub.2 O.sub.3 PC(OH)CH.sub.2 (CH.sub.3)PO.sub.3 H.sub.2 PA1 H.sub.2 O.sub.3 PC(CH.sub.3)(OH)(CH.sub.2).sub.4 C(CH.sub.3)(OH)PO.sub.3 H.sub.2 PA1 H.sub.2 O.sub.3 PC(OH)(C.sub.2 H.sub.5)C(OH)(C.sub.2 H.sub.5)PO.sub.3 H.sub.2 ##STR9## where R.sub.2 is a lower alkylene having from about one to about four carbon atoms, or an amine or hydroxy substituted lower alkylene; R.sub.3 is [R.sub.2 --PO.sub.3 M.sub.2 ] H, OH, amino, substituted amino, an alkyl having from one to six carbon atoms, a substituted alkyl of from one to six carbon atoms (e.g., OH, NH.sub.2 substituted) a mononuclear aromatic radical and a substituted mononuclear aromatic radical (e.g., OH, NH.sub.2 substituted); R.sub.4 is R.sub.3 or the group represented by the formula ##STR10## where R.sub.5 and R.sub.6 are each hydrogen, lower alkyl of from about one to six carbon atoms, a substituted lower alkyl (e.g., OH, NH.sub.2 substituted), hydrogen, hydroxyl, amino group, substituted amino group, a mononuclear aromatic radical, and a substituted mononuclear aromatic radical (e.g., OH and amine substituted); R is R.sub.5, R.sub.6, or the group R.sub.2 --PO.sub.3 M.sub.2 (R.sub.2 is as defined above); n is a number of from 1 through about 15; y is a number of from about 1 through about 14; and M is as earlier defined. PA1 N(CH.sub.2 PO.sub.3 H.sub.2).sub.3 PA1 NH(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 C.sub.4 H.sub.9 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 C.sub.10 H.sub.21 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 C.sub.15 H.sub.31 N(CH.sub.2 PO.sub.3 HNa)(CH.sub.2 PO.sub.3 Na.sub.2) PA1 C.sub.4 H.sub.9 N(CH.sub.2 CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 C.sub.4 H.sub.9 N(CH.sub.2 PO.sub.3 Na.sub.2).sub.2 PA1 C.sub.14 H.sub.29 N(CH.sub.2 PO.sub.3 (NH.sub.4).sub.2)CH.sub.2 PO.sub.3 HNH.sub.4 PA1 C.sub.6 H.sub.5 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 HOC.sub.6 H.sub.4 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 C.sub.6 H.sub.5 (CH.sub.2).sub.3 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 C.sub.6 H.sub.5 (CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 Na.sub.2).sub.2 PA1 (H.sub.2 O.sub.3 PCH.sub.2).sub.2 N(CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 (H.sub.2 O.sub.3 PCH.sub.2).sub.2 N(CH.sub.2).sub.3 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 (H.sub.2 O.sub.3 PCH.sub.2).sub.2 N(CH.sub.2).sub.7 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 (H.sub.2 O.sub.3 PCH.sub.2).sub.2 N(CH.sub.2).sub.10 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 (H.sub.2 O.sub.3 PCH.sub.2).sub.2 N(CH.sub.2).sub.14 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 (H.sub.2 O.sub.3 PCH.sub.2).sub.2 N(CH.sub.2).sub.2 NHCH.sub.2 PO.sub.3 H.sub.2 PA1 H.sub.2 O.sub.3 PCH.sub.2).sub.2 NH(CH.sub.2).sub.2 NHCH.sub.2 PO.sub.3 H.sub.2 PA1 C.sub.6 H.sub.13 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 (H.sub.2 O.sub.3 PCH.sub.2).sub.2 N(CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 H.sub.2)(CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 HO(CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 C.sub.6 H.sub.13 N(C(CH.sub.3).sub.2 PO.sub.3 H.sub.2)(CH.sub.2 PO.sub.3 H.sub.2) PA1 (HOCH.sub.2).sub.3 CN(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 (H.sub.2 O.sub.3 PCH.sub.2).sub.2 N(CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 H.sub.2)(CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 H.sub.2)(CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 HOCH.sub.2 CH.sub.2 N(CH.sub.2 PO.sub.3 H.sub.2)(CH.sub.2).sub.2 NH(CH.sub.2).sub.2 N(CH.sub.2 PO.sub.3 H.sub.2).sub.2 PA1 ClCH.sub.2 CH.sub.2 N((CH.sub.2 PO(OH).sub.2).sub.2 PA1 A. 2-phosphonobutane-1,2,4-tricarboxylic acid and PA1 B. 1-hydroxyethane-1,1-diphosphonic acid. PA1 1. Orthophosphate PA1 2. Pyrophosphate PA1 3. Tripolyphosphate PA1 4. Hexametaphosphate PA1 5. Higher molecular weight polyphosphate oligomers PA1 1. General--10 to 100 mg/liter (ppm) PA1 2. Preferred--10 to 50 mg/liter (ppm) PA1 3. Most preferred--15 to 40 mg/liter (ppm) PA1 1. General--4% to 80% PA1 2. Preferred--20 to 75% PA1 3. Most preferred--40 to 70% PA1 1. General--0.5:1 to 30:1 PA1 2. Preferred--0.5:1 to 10:1 PA1 3. Most preferred--1:1 to 4:1 PA1 1. 1,1 hydroxyethylidine diphosphonic acid and its salts PA1 2. 2-Phosphono butane 1,2,4-tricarboxylic acid and its salts PA1 1. General--0.5:1:0.33 to 30:1:16 PA1 2. Preferred--0.5:1:1 to 10:1:10 PA1 3. Most preferred--1:1:1 to 4:1:6
Inhibition of metal corrosion by oxygenated waters typically involves the formation of protective barriers on the metal surface. These barriers prevent oxygen from reaching the metal surface and causing metal oxidation. In order to function as a corrosion inhibitor, a chemical additive must facilitate this process such that an oxygen-impermeable barrier is formed and maintained. This can be done by interaction with either the cathodic or anodic half-cell reaction.
Inhibitors can interact with the anodic reaction (1) by causing the resultant Fe.sup.+2 to form an impermeable barrier, stifling further corrosion. This can be accomplished by including ingredients in the inhibitor compound which:
The reduction of oxygen at corrosion cathodes provides another means by which inhibitors can act. Reaction 2 represents the half cell in which oxygen is reduced during the corrosion process. The product of this reaction is the hydroxyl (OH.sup.-) ion. Because of this production of hydroxyl, the pH at the surface of metals undergoing oxygen-mediated corrosion is generally much higher than that of the surrounding medium. Many compounds are less soluble at elevated pH's. These compounds can precipitate at corrosion cathodes and act as effective inhibitors of corrosion if their precipitated form is impervious to oxygen and is electrically nonconductive.